Now, I'd like to know how they could be Christians when there was no Christ to follow. Perhaps TJF thinks Micah, Jeremiah, etc. were Christians, not Jews, just because of the idea that they were trumpeting Jesus's eventual arrival?

Setting aside the hilarity that is your stupid belief in an old Hebrew fairy tale, you're wrong even in the context of the laws of your fictional universe, in which Adam and Eve supposedly existed several thousand years BEFORE the birth and ministry of the character of Jesus. If you're going to believe nonsense, make it coherent nonsense.